This invention relates in general to a process for making nickel coated mandrels suitable for chromium coating for use in an electroforming process for the production of endless seamless nickel xerographic belts.
U.S. Pat. No. 3,905,400 discloses a cylindrically shaped hollow mandrel which is suitable in an electroforming process used for the production of endless seamless nickel xerographic belts. The mandrel comprises a core member which has a thin removable metal sleeve having a thickness between about 10 and 60 mils which is fitted over the core member to provide a surface for electroforming of nickel belts. The sleeve concept had certain shortcomings in that it was difficult to obtain a uniform surface between the nickel sleeve and the aluminum core. The solution in which the sleeve and core were being subjected tended to creep into the space between the sleeve and the aluminum core and form a galvanic cell where corrosion began. Since it is very difficult to obtain a perfect fit between the mandrel core and the sleeve, the surface area between the sleeve and the mandrel core would begin to corrode very quickly.
Prior to the instant invention, another method was used extensively for making mandrels suitable for use in electroforming processes for the production of endless seamless nickel xerographic belts. This was a process where aluminum mandrels were coated with a heavy, excess coating of chromium. Then these mandrels were ground down, i.e. machined, to within the size tolerances required for the mandrels, i.e. diameter, and to the roundness required in order to make the xerographic belt substrates. The plating of the chrome surfaces with excess chrome took about 15 to 20 hours. Then it would take about 15 hours grinding to reduce the thickness of the chrome outer surface of the mandrels to the proper dimensions. This was an expensive and time consuming process.
The instant process has advanced the art of making mandrels so that if the original core member, i.e. mandrel, is within the proper dimensions, then the core member is anodized and then a very thin layer of nickel is coated onto the core. The anodizing treatment of the aluminum core member, i.e. mandrel, forms a protective oxide film on the aluminum so that the aluminum core member can be placed into a subsequent nickel plating bath and the film will be inert to the bath long enough to get a protective layer of nickel plated onto the aluminum. After the nickel plating then a thin layer of chromium is deposited upon the nickel plated core member. This invention eliminates the necessity for the grinding step. The addition of the nickel and chromium layers prevent corrosion of the core member. Also, these layers enhance the good parting of metals when the endless seamless nickel xerographic belts are formed on the hollow core mandrels.
The reason for preferring chrome as an outer surface for the mandrel is that the belts to be made on the mandrels are, as mentioned, nickel. The nickel belts are plated onto the surface of the chrome plated mandrels. The chrome has a naturally occurring oxide and this makes the chrome surface resistive to the formation of a strongly adhering bond with the electro-deposited nickel. Therefore, when the nickel belt is electroplated onto the chromium surface, it is just a matter of having the right stress conditions and the belt slips right off of the mandrels. However, a nickel surface could be used for the mandrels. However, the nickel would have to be passivated periodically, i.e. the nickel surface would have to be nickel oxide, since nickel can be plated onto nickel oxide and these layers will separate without bonding. However, the nickel oxide would be reduced during each cycle. Therefore, a chromium plate surface for the mandrel is preferred since the electrolyte of the nickel bath for the formation of the nickel belts does not reduce the chromium oxide layer. Therefore, the process can continue for many cycles since the chromium oxide is not disturbed.